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Use idiomatic CLZ implementation #582

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solidpixel merged 1 commit into from
Sep 3, 2025
Merged

Use idiomatic CLZ implementation #582

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70 changes: 10 additions & 60 deletions Source/astcenc_mathlib_softfloat.cpp
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
// SPDX-License-Identifier: Apache-2.0
// ----------------------------------------------------------------------------
// Copyright 2011-2021 Arm Limited
// Copyright 2011-2021,2025 Arm Limited
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy
Expand Down Expand Up @@ -30,69 +30,19 @@ typedef uint16_t sf16;
typedef uint32_t sf32;

/******************************************
helper functions and their lookup tables
helper functions
******************************************/
/* count leading zeros functions. Only used when the input is nonzero. */

#if defined(__GNUC__) && (defined(__i386) || defined(__amd64))
#elif defined(__arm__) && defined(__ARMCC_VERSION)
#elif defined(__arm__) && defined(__GNUC__)
#else
/* table used for the slow default versions. */
static const uint8_t clz_table[256] =
{
8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
#endif

/*
32-bit count-leading-zeros function: use the Assembly instruction whenever possible. */
/* Idiomatic count-leading zeros, generates native instruction on modern compilers. */
static uint32_t clz32(uint32_t inp)
{
#if defined(__GNUC__) && (defined(__i386) || defined(__amd64))
uint32_t bsr;
__asm__("bsrl %1, %0": "=r"(bsr):"r"(inp | 1));
return 31 - bsr;
#else
#if defined(__arm__) && defined(__ARMCC_VERSION)
return __clz(inp); /* armcc builtin */
#else
#if defined(__arm__) && defined(__GNUC__)
uint32_t lz;
__asm__("clz %0, %1": "=r"(lz):"r"(inp));
return lz;
#else
/* slow default version */
uint32_t summa = 24;
if (inp >= UINT32_C(0x10000))
{
inp >>= 16;
summa -= 16;
}
if (inp >= UINT32_C(0x100))
{
inp >>= 8;
summa -= 8;
}
return summa + clz_table[inp];
#endif
#endif
#endif
uint32_t count = 32;
while (inp)
{
inp >>= 1;
count--;
}
return count;
}

/* the five rounding modes that IEEE-754r defines */
Expand Down